1. Field of the Invention
This invention relates to apparatus and methods for reading and writing data on storage media such as magnetic tape.
2. Background of the Invention
In most tape drives, magnetic tape is passed between spools and over guiding elements such as rollers in order to direct the magnetic tape across a read/write head. The read/write head typically includes a number of write elements to write tracks on the magnetic tape, and an equivalent number of read elements to read back data from the magnetic tape as it is written. This allows the written data to be verified as it is written. In order to provide some leeway when reading back data, the read elements are typically narrower than the write elements, and thus narrower than the tracks they are reading back. This allows the read elements to read back data even if they are not exactly centered over the written tracks. However, if the misalignment between the read elements and the center of the written tracks is enough, a point may be reached where the read elements can no longer accurately read back the data.
The misalignment between the read elements and written tracks, which is generally caused by angular misalignment of the read/write head relative to the magnetic tape, is typically referred to as “skew.” The greater angular misalignment of the read/write head relative to the tape, the greater the skew. As alluded to above, if the skew is large enough, the read elements may no longer be able to read back data from the magnetic tape.
In some tape drives, such as some LTO tape drives, the angle of the read/write head can be manually adjusted relative to the tape in order to minimize the skew. Unfortunately, shifts in the tape stack can cause the skew readings to change as the magnetic tape traverses across the head. Thus, adjusting the angle of the read/write head or the magnetic tape to minimize the skew can be like hitting a moving target. That is, a technician may adjust the angle to minimize the skew only to find that the skew later increases due to variations in the tape stack. Thus, a technician may have difficulty finding an optimal angular position for the tape head relative to the magnetic tape.
In view of the foregoing, what are needed are apparatus and methods for adjusting skew in the presence of tape motion. Ideally, such an apparatus and method will enable a technician to easily adjust the angular position of a tape head relative to the magnetic tape even while the tape is in motion.